A foundry core or mold of sand-containing molding materials with an inorganic binding system is hardened in a core box by exposure to a temperature predetermined for hardening the core or the mold.
It is standard in the so-called hot-box method to mix organic additives, such as for instance a phenol-based binding agent, with sand to make a wet core and to harden it in a mold by heating the mold to temperatures ranging from 200 to 270° C. Such a system can be very fast. The alternative is the cold-box method as described for example in U.S. Pat. No. 3,409,570 where the hardening takes place over hours or days and is typically effected by gasification. The hot-box method produces a somewhat weaker core, but is very fast, its main disadvantage being that it produces a considerable amount of noxious and even toxic emissions.